vant-weapp/packages/tag/index.ts

import { VantComponent } from '../common/component';
import { RED, BLUE, GREEN } from '../common/color';

const DEFAULT_COLOR = '#999';
const COLOR_MAP = {
  danger: RED,
  primary: BLUE,
  success: GREEN
};

type Style = {
  [key: string]: string;
};

VantComponent({
  props: {
    size: String,
    type: String,
    mark: Boolean,
    color: String,
    plain: Boolean,
    round: Boolean,
    textColor: String
  },

  computed: {
    style() {
      const color = this.data.color || COLOR_MAP[this.data.type] || DEFAULT_COLOR;
      const key = this.data.plain ? 'color' : 'background-color';
      const style = { [key]: color } as Style;

      if (this.data.textColor) {
        style.color = this.data.textColor;
      }

      return Object.keys(style).map(key => `${key}: ${style[key]}`).join(';');
    }
  }
});